Wireless transmission for local area networks (WLAN) is in the meanwhile a well established technology for end users. An essential part of a local area network is a residential gateway connecting the local area network to the Internet. A mechanism for connecting wireless devices to a local area network is called Wi-Fi, which is a brand name for devices using the IEEE 802.11 family of standards for wireless transmission. The IEEE 802.11 standards, also called recommendations, define a residential gateway as a wireless access point, and a wireless device connected to the residential gateway is called a station. The IEEE 802.11 standards are defined such that wireless devices distributed all over a home can be connected to the residential gateway without requiring any data cables.
The IEEE 802.11b and 802.11g standards use the 2.4 GHZ ISM band, wherein the later developed 802.11g standard allows a data rate of up to 54 Mbit/s, which is even sufficient in principle for providing high quality video streaming for real time applications. But the Wi-Fi technology has become victim of its own success: even though there are several non-overlapping frequency channels that can be chosen for data transmission (four in Europe, three in US), interference from neighbouring Wi-Fi devices has become a serious problem in urban areas. In addition, there are also other devices using the 2.4 GHZ ISM band, for example Bluetooth devices, microwave ovens, babyphones and others.
It is therefore a consensus in the industry that video streaming over the 2.4 GHz ISM band will not work reliably, and that the 5 GHz U-NII band has to be used for avoiding interference. Further, the present 802.11g wireless devices are designed for data transport and do not have high quality video transmission in mind. They operate with a maximum physical layer bit rate of 54 Mbit/s, which provides about 22 Mbit/s average data throughput. In the meanwhile first companies producing Wi-Fi devices have started to work on dedicated 5 GHz Wi-Fi solutions, tuned specifically for video applications in accordance with the new IEEE 802.11n standard, which allow to specify a sufficient throughput and packet loss for a given radio frequency path in the 5 GHz band.
But for a user interested in such an application there is still the remaining problem, that he does not have any information about the RF path loss between a station and an access point intended for video transmission in his home. There exists also no reliable model to calculate the RF path loss based on the distance between the station and the access point including additional path loss by walls, cabinets or other obstacles. For example, the attenuation caused by a conventional concrete floor can be about 5 dB, but may be as well as 25 dB in case the concrete floor contains metallic screed reinforcement mesh, which is not visible to the user.
A user owns for example a Wi-Fi access point AP operating in the 2.4 GHz band in a room R1 of his home and a station STA1 in a room R2 at a location L1, e.g. a computer, as shown in FIG. 1. But he wishes to replace the current access point AP by an advanced 5 GHz video over Wi-Fi access point AP2, a residential gateway operating in the 5 GHz U-NII band, and use it with a 5 GHz video over Wi-Fi set-top box STA2 at a location L2. The set-top box STA2 has to be located close to a television set TV in the room R2.
Although the documentation of the new 5 GHz access point AP2 promises that it can guaranty a data throughput of 40 Mb/s and a packet loss below 10-16 packets/sec up to a path loss of 90 db, which allows viewing and recording of two different high resolution movies simultaneously, the user has no information whether the solution would actually work sufficiently in his house at the locations that he envisages for the residential gateway AP2 and the set-top box STA2. In the room R1, there may exist for example a chimney or a large cabinet C in the direct line between the residential gateway AP2 and the set-top box STA2. So the only way to find out would be either to buy the equipment in a store and hope that it operates at the wanted locations, or to have a site service conducted by the company offering the new access point AP2, if possible.
U.S. Pat. No. 7,317,419 describes a method for estimating a position of a target device emitting a radio frequency signal based on data pertaining to strength of an emission received from the target device. The position of the target device is estimated based on receive signal strength data associated with received emissions from the target device and from reference devices. The target device can be for example a device emitting energy that interferes with the operation of IEEE 802.11 WLAN devices, e.g. a microwave oven, a Bluetooth device or a cordless telephone. The method uses multiple path loss models, e.g. a path loss model for areas with low obstruction densities, and another path loss model for high obstruction densities. The specific coefficients for the path loss models can be found empirically.